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Port Checker

Enter a hostname and port number to test if the port is accessible from the internet.

Updated

Common ports:

Server-side TCP check — tests external port accessibility from our servers.

No check run yet

Enter a host and port, then check to see the result here.

How to use Port Checker

The Port Checker tests whether a specific TCP port on a server is open and accepting connections from the public internet. Services listen on ports — web servers on 80 and 443, mail on 25 and 587, SSH on 22 — and a port that appears closed from outside is the classic symptom of a firewall rule, a service that is not running, or a router that is not forwarding traffic. Use this tool to confirm that a service you just deployed is actually reachable, or to verify that a port you expect to be blocked really is closed to the outside world.

  1. Enter the server hostname or IP address you want to test.
  2. Enter the port number, or pick a well-known service port.
  3. Click Check to attempt a TCP connection from our servers.
  4. Read whether the port is open (accepting connections) or closed/filtered.
  5. Adjust your firewall or service configuration and re-test as needed.

Open, closed and filtered ports

A port can be in one of three states. Open means a service accepted the connection. Closed means the host replied but nothing is listening on that port. Filtered means a firewall silently dropped the probe, so no reply came back at all and the attempt times out. The difference matters: a closed port suggests the service simply is not running, while a filtered port points to a firewall or security group actively blocking access. This tool reports which behaviour it observed so you can target the right fix.

Common ports and their services

Most everyday services use well-known port numbers, and memorising the common ones speeds up troubleshooting. Web traffic uses 80 and 443, SSH uses 22, and the various mail protocols spread across 25, 465, 587, 110, 143, 993 and 995. When a service is unreachable, the first check is whether its standard port is open from outside; if it is closed but the service is running locally, the problem is almost always a firewall or port-forwarding rule in between.

Well-known ports
PortService
22SSH
80HTTP
443HTTPS
25 / 587SMTP (mail)
3306MySQL

Glossary

TCP port
A numbered endpoint on a host that a network service listens on for connections.
Open port
A port where a service accepted an incoming connection.
Filtered port
A port where a firewall dropped the probe, producing no response.
Firewall
A system that allows or blocks network traffic according to rules.
Port forwarding
A router rule that directs external traffic on a port to a specific internal host.

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